The present invention relates to a method for the chemothermal conversion of fluid compounds or compounds which are convertible into a fluid state, and to a converter for the performance of the method.
The protection of the environment gains more and more importance, and correspondingly, emission restrictions are becoming stricter and stricter. Incineration and other thermal processes are still the most common ways of eliminating waste or substances by means of thermal destruction. The efficiency rate of thermal destruction has therefore to become much higher, in order to meet the new demands.
As an example, according to the very common German regulation, not more than 1.5 nanogram of dioxins per m3 is allowed as an average emission. In order to meet this regulation, thermal destruction has to have an efficiency rate of at least 99.9999985%. A maximum of 0.0000015% of the compounds is allowed to be incompletely destroyed in order to reach such a high efficiency rate.
At the same time, it is not only necessary to reach such a high rate of efficiency, but also, in order to open all of the molecular bonds, a high temperature is necessary. For example, fluoro-chloro-hydrocarbons are extremely temperature stable, and require a temperature higher than 1,900xc2x0 to be cracked. To reach this aim, very often a temperature is chosen that can open all molecular bonds. The molecular structures are then replaced by an ionic structure or form called xe2x80x9cplasma.xe2x80x9d Such a structure can also be a mixture wherein some of the molecules are already in an ionic form and other, more stable molecular structures are still intact. In such an event, the structure will be called a xe2x80x9cplasma-like structurexe2x80x9d or form.
The highest temperature level or temperature is required for the initial opening of the molecular bonds, and must be achieved first.
To reach the required efficiency rate, the temperature has to be distributed in such as way that there is no colder zone where molecules could pass through without being cracked into atoms. Thus, a flame geometry ensuring sufficient heat distribution is also essential to obtaining a high efficiency rate.
In order to achieve efficient thermal destruction at an industrial scale and not just in a laboratory device, these three tasks: high efficiency rate, sufficient heat distribution, and sufficient high temperature, must be realized at reasonable cost.
There are certain physical phenomena and effects that limit reaction possibilities in burners, burner systems, or similar systems and devices. An exothermic chemical reaction creates a certain amount of energy. This energy is set free with the chemical reaction and at the location of the reaction. The energy leads to a specific temperature, depending upon the volume, mass, and distance to the point of the chemical reaction. The closer to the point of reaction, the higher is the temperature. The largest part of the energy is released in the form of radiation, especially infrared radiation, spreading from the point where the chemical reaction takes place. The temperature, as a function of the heat, can also be connected to this radiation. Thus, the temperature decreases exponentially with the exponential increase of the spherical surface of distribution of the heat radiation.
Only a complete exothermic chemical reaction leads to a complete conversion of the compounds. If other compounds or, for example, a feedstock, interferes with the exothermic chemical reaction, then part of the exothermic reaction will not take place. Normally, in a continuous exothermic reaction, a molecule or molecules which have just been converted in the exothermic reaction or have reacted, will send energy to the following molecules of the continuous exothermic reaction partner and will initiate or ignite another reaction. If the other compounds are mixed with the main one, the main reaction will be incomplete and/or insufficient. A feedstock might shield and partly interrupt the exothermic reaction. In such a case, the requested and targeted efficiency rate of 99.9999985% cannot be achieved.
Consequently, the exothermic chemical reaction and the feeding of the compound to be destroyed have to be carried out at different places or times. First, the exothermic chemical reaction must be completed, and only then the next compound that is in need of the exothermic energy may be added.
Burner systems intended to destroy compounds by means of an exothermic chemical reaction therefore feed the first compound to be destroyed after the first exothermic reaction, and afterwards feed the second compound or mixture of compounds. In this way, the reactions are completed by the various burner systems and the presence of residues of the basic reaction in their flue gases is avoided.
It can be seen in prior art references that it is an acknowledged necessity to complete the first exothermic reaction before further compounds or feedstock are introduced for thermal destruction. It is not important whether the thermal destruction is for the purpose of destroying substances or compounds, or whether it is intended to create new ones and the destruction of a molecular structure is only a necessary step of a more complex reaction or series of reactions.
In the drawings of U.S. Pat. No. 2,934,410 (G. H. Smith), it can clearly be seen that the two-zone burner is divided into an upper area wherein the exothermic reaction takes place and is completed, and a lower, secondary area wherein the stock or further compounds are fed into the burner.
The earlier U.S. Pat. No. 3,098,883 (O. Heuse), describes and shows that the reaction has a first, exothermic portion divided into several parts, which is followed by a second, also divided, step wherein the provided energy is used to open molecular bonds. In the case of the patent to Heuse, the energy is intended to create or produce new substances with the aid of the energy released at a high temperature from the primary reaction step. This patent also describes the need for short flames, in order not to cause a decrease of temperature by losing much of the energy.
A short flame is short because the exothermic reaction inside the flame is fast. Heuse also indicated that the exothermic reaction first has to be completely terminated before the secondary step is started. This is also clear from the drawings, wherein it can be seen that the first exothermic reaction takes place at a separate portion of the apparatus, and especially from the technical detail that the fuel and oxidizing gas are introduced separately into the apparatus. The apparatus of Heuse, therefore, also requires allowing the compounds of the exothermic reaction to react in the first portion, and only then adding the next compound in the further portion. The difference with respect to the more basic concept of Smith is that Smith divides the stream of introduced gases into several smaller streams, together with the option of giving these streams a spin to produce additional kinetic energy and introducing these gases tangentially, creating a rotation that assists in mixing the combustion gases of the first exothermic reaction with the compounds of, or for, the secondary reaction.
Both of these prior art U.S. patents clearly show a burner device and procedure having two steps following each other, involving a first, exothermic reaction followed by a secondary reaction. Overlapping of these reactions is not intended. Most known burners and burner devices use this principle.
In U.S. Pat. No. 4,007,002 (Robert M. Schirmer), describing combustors and methods of their operation, the same principle is used. A first reaction is completed and is even covered by an inner housing, in order to avoid contact of the gases of the first reaction with the compounds of the second reaction before the first reaction is completed.
Conventional burners and similar devices that use an exothermic reaction to gain energy have in common that they, by different means, complete the preliminary exothermic reaction first before they begin the next step, either destruction of the molecules, production of hot combustion gases, or any other purpose they may have. In order to reach high temperatures for the second reaction, all of these devices have a consequent disadvantage in that they cannot utilize a substantial portion of the energy created in the first step.
When the exothermic first reaction takes place, energy is released. This energy is, as described above, partly released in the form of body heat: the molecules of the combustion gases or products that were created in the exothermic reaction have a higher temperature. The largest part of the energy is released in the form of radiation, mainly infrared radiation, going out from the location of the reaction and radiating in a spherical form. When the distance to the location where the infrared radiation is created is longer, there is a lower temperature, due to the larger volume of space that is covered. With linear increase of the distance (the radius of the spherical radiation), the surfaces increase exponentially, as well as the volume. In this manner, the temperature gained from the radiation from the first exothermic reaction decreases exponentially with the distance to the location of the reaction.
In the case of a burner or apparatus like that described by Smith, more than 80% of the total energy that has been created in the first step, the exothermic reaction, cannot be used in the secondary step where further compounds are added. Only the small section of the spherical heat radiation which overlaps with the surface of the cross-section of the entrance to the second chamber can be used. All the rest of the energy is lost for the secondary reaction. Hence, the temperature that can be reached with the specific amount of energy introduced into the system by the compounds of the first exothermic reaction is much lower than it could theoretically be.
Another side effect is that because the secondary reaction takes place at a location away from the hottest point, the secondary reaction cannot be as complete as it would be at a higher temperature close to the first exothermic reaction. The system therefore might also not reach the required efficiency rate of 99.9999985%. In a case where insufficient burner systems are used, in order to reach the required efficiency rate, a secondary burner system, called an xe2x80x9cafter-burner,xe2x80x9d is added. Secondary or after-burner systems also require fuel and control, and lead to an increase in investment and operating costs. In addition, they produce a higher output of carbon dioxide, which should be avoided.
The object of the present invention is to provide a burner system that allows a continuous, high temperature, exothermic reaction using the heat radiation at the highest possible temperature without interrupting or disturbing the exothermic chemical reaction.
The present invention provides a system that, with one burner, can reach the necessary high temperature and required efficiency rate. In several independently documented tests, it has been shown that the system of the present invention is able to reach an efficiency rate of 99.99999987% (ten times better than required) in a single step. The system of the invention is operable on an industrial scale.
The present invention achieves the above objects by providing, in a method of chemothermal conversion of feedstock in the form of fluid compounds or compounds convertible into a fluid state, into low-molecular, organic or inorganic compounds, said method comprising at least one first, preliminary step in which reaction compounds under excess pressure are caused to flow through a first mixing channel having a reduced flow cross-section, in which said compounds are completely intermixed to form an exothermic first mixture but are unable to inter-react within said first mixing channel; at least one simultaneous, second preliminary step in which said feedstock, either alone or in a mixture with one or more other substances under excess pressure, is caused to flow through a second mixing channel having a reduced flow cross-section, in which said compounds are completely intermixed to form a second mixture but are unable to inter-react within said second mixing channel; wherein compounds of said first preliminary step, downstream of said first mixing channel, and after reduction in flow speed produced by an increase in flow cross-section, flow into a reaction chamber, and perform an exothermic reaction with each other, still under excess pressure, at a very high reaction speed and very high energy density, dependent on said excess pressure, thereby creating a field of high temperature and heat radiation; wherein compounds of said second preliminary step, downstream of said second mixing channel, and after reduction in flow speed produced by an increase in flow cross-section, flow into the same reaction chamber, and wherein the compounds of said second preliminary step then receive sufficient energy from the exothermic reaction of the compounds of the first preliminary step to react in such a way that the molecular structure of the compounds of said second preliminary step is completely destroyed; the improvement comprising reaching an extremely high efficiency rate of the destruction of the compounds of the second preliminary step by introducing the compounds of said first preliminary step through at least one small mixing channel under excess pressure of between 1.5 atmospheres and 150 atmospheres, so that the start of the exothermic reaction is delayed until the compounds reach said main reaction chamber, wherein, due to the excess pressure, the compounds react very quickly in an explosion-like manner, thereby reaching a high temperature and high density of heat radiation immediately usable for the destruction of the molecular structure of the compounds of said second preliminary step, and introducing the compounds of said second preliminary step simultaneously with the compounds of said first preliminary step at the downstream end of the mixing channels of said first preliminary step where said exothermic reaction takes place, thus enabling the transfer of energy from the exothermic reaction of the compounds of said first preliminary step at a highest possible temperature and heat radiation level to the compounds of said second preliminary step.
The invention further provides a converter for the chemo-thermal conversion of feedstock, said converter comprising a main reaction chamber with an exit nozzle for reaction products; at least one first charging unit for feeding a first gas mixture into said reaction chamber and at least one second charging unit for feeding a second gas mixture into said main reaction chamber, each said charging unit comprising means defining a plurality of feed ducts for the separate feeding of components of each respective mixture, and means defining a mixing channel connected with said main reaction chamber, said mixing channel serving as a mixing region for formation of a mixture of said feed components, the flow cross-section of said channel being selected to be so reduced in size that the speed of flow of the mixture in the mixing channel is greater than the speed of propagation of any reaction front of the components of the mixture therein, whereby flashback from said reaction chamber is prevented.